This proposal seeks to investigate the in vivo role of tag I (transiently expressed axon glycoprotein) through the generation and analysis of transgenic zebrafish (Danio rerio that can be produced to misexpress this molecule at specific stages of development. tag I is a cell adhesion molecule of the immunoglobulin superfamily that is expressed transiently by a subset of embryonic cells and serves as a fertile substrate for neurite outgrowth in vitro. Its pattern of expression in the differentiating neurons has implicated it in the processes of axon outgrowth, selective fasciculation, target recognition and cell migration. Although homologs of zebrafish tag I have been cloned in the rat (TAG-1), chick (axonin 1), and human(TAX-1), the in vivo role of this moIecule has seen limited analysis. The zebrafish represents an ideal model system to investigate the function of tag I because it is a vertebrate embryo that is amenable to a variety of cellular, molecular and genetic techniques. This proposal seeks to 1) construct zebrafish tag I transgenes that have been linked to green fluorescent protein(GFP) and are driven by the zebrafish at shock promoter; 2) create stable transgenic lines harboring these constructs; and 3) analyze the consequences of misexpressing tag I at different stages of development. A better understanding of the precise role tag I plays in neuronal development could increase our understanding of how the intricate connections of the nervous system are established, as well as suggest means for therapeutic intervention after neuronal injury. Funding through this AREA grant will allow unique learning experiences for undergraduates and facilitate the principal investigator's transition to an independent investigator.